What kind of end result are you looking for? Are you making RGB images that you want to visually match some printed materials? Are you trying to match RGB colors that will be used in print materials?
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DA01Aug 10 '11 at 21:46

3 Answers
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To answer your second question first, Pantone is a color-matching system, like Trumatch or Toyo. It's just a standard so everybody can agree on what "kelly green" is.

In Photoshop, click on the Set Foreground Color box in the vertical toolbar. When the Color Picker comes up, click on Color Libraries. In the dropdown menu at the top of the box, you have a slew of Pantone libraries (which are just groups of swatches). So you have various sets of pastels, metallics, process, and solid colors, which shift slightly depending on whether you're printing on coated or uncoated paper.

In Illustrator, go under Window and select Swatches. In the Swatches palette, click on the Options icon (the three lines with the down arrow, not the two right arrows) and scroll down to Open Swatch Library. From there select Color Books. (Yes, Illustrator is annoying this way.) The same list as in Photoshop should pop up.

To get the RGB values for the tint? Honestly, I'd cheat. In Photoshop, I'd select my Pantone color (for the sake of argument, Pantone 123, a sunny yellow). Make an new document 100 pixels square and fill it with the yellow. Under Layers, change the opacity to 50%. Flatten it. Eyedropper the result. I get 255/227/150.

Great answer, but I don't own photoshop. Can this be done with GIMP or some free downloadable product?
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P.Brian.MackeyAug 10 '11 at 18:23

I would imagine so, but I've never used GIMP.
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Lauren IpsumAug 10 '11 at 18:24

According to wiki it can't be done with free/low cost software "Pantone asserts that their lists of color numbers and pigment values are the intellectual property of Pantone and free use of the list is not allowed.[11] This is frequently held as a reason why Pantone colors cannot be supported in Open Source software such as GNU Image Manipulation Program (GIMP) and are not often found in low-cost software."
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P.Brian.MackeyAug 10 '11 at 18:26

You don't say what the end product is supposed to be, so I can only give with limited advice.

To find specific Pantone colors as RGB swatches, use this page on the Pantone website. Since you have the RGB values already, you could also just type them into the color picker of the gimp (or equivalent).

To get tints, follow Lauren's suggestion, starting with the RGB values from your specification sheet. Use the equivalent procedure in whatever RGB image editing software you have available.

Your most accurate and certain course would be to purchase the Pantone Solids swatch book, but if everything you are producing will be seen only on a monitor or mobile device, accuracy is neither attainable (since you have no way to calibrate the viewer's screen) nor much of an issue.

To get an approximation to the RGB of the tint value, you need a bit of arithmetic:

If the RGB of your Pantone colour is (0, 101, 96)
and the background is pure white, i.e. (255,255,255)

then a 50% tint is pretty much halfway between the two - and that calculation is done for each of R,G,B separately. And the answer is: R=127, G=178, B=176 . That's because 127 is about halfway between 0 and 255. 178 is halfway between 101 and 255. 176 is about halfway between 96 and 255.

To get a tint of N (where N is in the range 0.01 to 0.99; 0.01=1%, 0.99=99%): for each colour value X in RGB, take [N x X] + [ (1-N) x 255], to get the RGB value of your tint.

So, if you wanted a 30% tint of your (0,101,96), 30% = 0.30

So, R = [0.3 x 0] + [ (1-0.3) x 255] = 0 + 179 = 179

and G = [0.3 x 101] + [ (1-0.3) x 255] = 30 + 179 = 209

and B = [0.3 x 96] + [ (1-0.3) x 255] = 29 + 179 = 208

i.e. RGB = (179, 209, 208)

But remember - when you convert between Pantone and RGB; or between Pantone and CMYK, you're going to change colours a bit. Every time. What "the right thing" to do is, will depend completely on what your end use is.

Are you by any chance creating an application for a monitor (e.g. a web page), based on a corporate colour scheme that's specified in Pantone colours? That's one of the few occasions where converting from Pantone to RGB would be a safe thing to do - because it's inevitable, it has to be done, because the end user is going to see it as RGB.

If it's for any print application, then use an application (such as InDesign, Illustrator, Photoshop) that will preserve the Pantone number, and tints, in that form.